Traction control circuits have been incorporated into anti-lock brake system to provide a way of synchronizing the rotational spin of the wheels of a vehicle. U.S. Pat. Nos. 4,778,225, 5,096,267 and 5,176,433 illustrate structure to accomplish such traction control in a manner acceptable most vehicle operators. The output force developed by the vacuum brake boosters in these brake systems has been achieved through the pressure differential developed between a front chamber and a rear cheer. In some instances it may be desirable to obtain greater output force from the vacuum brake booster however space constraints with respect to the location in a vehicle do not provide for any greater diameter in the movable wall. To meet such need in an increase in the output force it has been common to replace a brake booster having a single movable wall with a brake booster having two movable walls such as the disclosed in U.S. Pat. No. 5,233,911. However such a tandem brake booster would need to be modified if a traction control is incorporated into the brake system. U.S. Pat. No. 3,559,532 discloses a tandem brake booster which has been modified by placing various conduits on the outside of the housing communicate vacuum and atmosphere to the front and rear cheers. Unfortunately these additional conduits also take up space and are unprotected from damage that may occur in some vehicles. In the brake booster disclosed in U.K. Patent 2,230,580 the addition of the traction control feature was achieved through a separate actuation unit located between the tandem movable wall and as such would add additional overall length to the vacuum brake booster assembly.